IndexNulls, propriété – Exemple (VC++)

S’applique à : Access 2013, Office 2013

Cet exemple illustre la propriété IndexNulls d’un objet Index. Le code crée un index et définit la valeur de IndexNulls en fonction de l’entrée utilisateur. Ensuite, l’index est ajouté à la tableEmployees dans le catalogueNorthwind. Le nouvel objet Index est appliqué à un objet Recordset basé sur la table Employees et le Recordset est ouvert. Un nouvel enregistrement est ajouté à la table Employees, avec la valeur Null dans le champ indexé. Selon le paramètre de la propriété IndexNulls, ce nouvel enregistrement est affiché ou non.

 
// BeignIndexNullCpp 
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" rename("EOF", "EndOfFile") 
#import "c:\Program Files\Common Files\system\ado\msadox.dll" no_namespace 
 
#include "iostream.h" 
#include "stdio.h" 
#include "conio.h" 
#include "ADOXIndexNullsX.h" 
 
// Function declarations 
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);}; 
void IndexNullsX(_bstr_t); 
 
////////////////////////////////////////////////////////// 
// // 
// Main Function // 
// // 
////////////////////////////////////////////////////////// 
void main() 
{ 
 if(FAILED(::CoInitialize(NULL))) 
 return; 
 
 printf("\nShow records having indexed field value = NULL? (Y/N):"); 
 char input = getche(); 
 
 if(toupper(input)=='Y') 
 { 
 IndexNullsX("Allow"); 
 } 
 else if(toupper(input)=='N') 
 { 
 IndexNullsX("Ignore"); 
 } 
 else 
 { 
 exit(0); 
 } 
 
 ::CoUninitialize(); 
} 
 
////////////////////////////////////////////////////////// 
// // 
// IndexNullsX Function // 
// // 
////////////////////////////////////////////////////////// 
void IndexNullsX(_bstr_t strSel) 
{ 
 HRESULT hr = S_OK; 
 
 // Define ADOX object pointers. 
 // Initialize pointers on define. 
 // These are in the ADOX:: namespace. 
 _CatalogPtr m_pCatalog = NULL; 
 _IndexPtr m_pIndexNew = NULL; 
 
 // Define ADODB object pointers 
 ADODB::_ConnectionPtr m_pCnn = NULL; 
 ADODB::_RecordsetPtr m_pRstEmployees = NULL; 
 
 // Define other variables 
 IADORecordBinding *picRs = NULL; // Interface Pointer Declared 
 CEmployeeRs emprs; // C++ Class Object 
 
 // Define string variable. 
 _bstr_t strCnn("Provider='Microsoft.JET.OLEDB.4.0';" 
 "data source='c:\\Program Files\\Microsoft Office\\Office\\" 
 "Samples\\Northwind.mdb';"); 
 
 try 
 { 
 TESTHR(hr = m_pCnn.CreateInstance(__uuidof(ADODB::Connection))); 
 TESTHR(hr = m_pCatalog.CreateInstance(__uuidof (Catalog))); 
 TESTHR(hr = m_pIndexNew.CreateInstance(__uuidof(Index))); 
 TESTHR(hr = m_pRstEmployees.CreateInstance( 
 __uuidof(ADODB::Recordset))); 
 
 // Connect the catalog. 
 m_pCnn->Open(strCnn,"","",NULL); 
 m_pCatalog->PutActiveConnection(_variant_t((IDispatch *)m_pCnn)); 
 
 // Append Country column to new index. 
 m_pIndexNew->Columns->Append("Country",adVarWChar,0); 
 m_pIndexNew->Name = "NewIndex"; 
 
 // Set IndexNulls based on user input 
 if(strcmp((LPSTR)strSel,"Allow")==0) 
 { 
 m_pIndexNew->IndexNulls = adIndexNullsAllow; 
 } 
 else if(strcmp((LPSTR)strSel,"Ignore")==0) 
 { 
 m_pIndexNew->IndexNulls = adIndexNullsIgnore; 
 } 
 
 // Append new index to Employees table 
 m_pCatalog->Tables->GetItem("Employees")->Indexes->Append( 
 _variant_t((IDispatch *)m_pIndexNew)); 
 m_pRstEmployees->Index = m_pIndexNew->Name; 
 m_pRstEmployees->Open("Employees", 
 _variant_t((IDispatch *)m_pCnn), 
 ADODB::adOpenKeyset,ADODB::adLockOptimistic, 
 ADODB::adCmdTableDirect); 
 
 // Add a new record to the Employees table. 
 m_pRstEmployees->AddNew(); 
 m_pRstEmployees->Fields->GetItem("FirstName")->Value = 
 (_bstr_t) "Gary"; 
 m_pRstEmployees->Fields->GetItem("LastName")->Value = 
 (_bstr_t) "Haarsager"; 
 m_pRstEmployees->Update(); 
 
 // Bookmark the newly added record. 
 _variant_t varBookmark = m_pRstEmployees->Bookmark; 
 
 // Use the new index to set the order of the records. 
 m_pRstEmployees->MoveFirst(); 
 printf("\n\nIndex = %s,",(LPSTR) m_pRstEmployees->Index); 
 printf("IndexNulls = %d\n\n",m_pIndexNew->IndexNulls); 
 cout<<"Country - Name"<<endl; 
 
 // Open an IADORecordBinding interface pointer which 
 // we will use for binding Recordset to a class 
 TESTHR(hr = m_pRstEmployees->QueryInterface( 
 __uuidof(IADORecordBinding),(LPVOID*)&picRs)); 
 
 // Bind the Recordset to a C++ class here 
 TESTHR(hr = picRs->BindToRecordset(&emprs)); 
 
 // Enumerate the Recordset.The value of the 
 // IndexNulls property will determine if the newly 
 // added record appears in the output. 
 while(!(m_pRstEmployees->EndOfFile)) 
 { 
 printf("%s - %s %s\n", 
 emprs.lemp_CountryStatus == adFldOK ? 
 emprs.m_szemp_Country :"[Null]", 
 emprs.lemp_FirstNameStatus == adFldOK ? 
 emprs.m_szemp_FirstName :"<NULL>", 
 emprs.lemp_LastNameStatus == adFldOK ? 
 emprs.m_szemp_LastName :"<NULL>"); 
 m_pRstEmployees->MoveNext(); 
 } 
 
 // Delete new record because this is a demonstration. 
 m_pRstEmployees->Bookmark = varBookmark; 
 m_pRstEmployees->Delete(ADODB::adAffectCurrent); 
 } 
 catch(_com_error &e) 
 { 
 // Notify the user of errors if any. 
 _bstr_t bstrSource(e.Source()); 
 _bstr_t bstrDescription(e.Description()); 
 
 printf("\n\tSource : %s \n\tdescription : %s \n ", 
 (LPCSTR)bstrSource,(LPCSTR)bstrDescription); 
 } 
 catch(...) 
 { 
 cout << "Error occured in include files...."<< endl; 
 } 
 
 if (m_pRstEmployees) 
 { 
 if (m_pRstEmployees->State == 1) 
 { 
 m_pRstEmployees->Close(); 
 m_pRstEmployees = NULL; 
 } 
 } 
 
 // Delete new Index because this is a demonstration. 
 if (m_pCatalog) 
 m_pCatalog->Tables->GetItem("Employees")->Indexes-> 
 Delete(m_pIndexNew->Name); 
 
 if (m_pCnn) 
 { 
 if (m_pCnn->State == 1) 
 { 
 m_pCnn->Close(); 
 m_pCnn = NULL; 
 } 
 } 
 
 m_pCatalog = NULL; 
} 
// EndIndexNullCpp 

IndexNullX.h

    // BeginIndexNullsH 
    // IndexNullsX.h 
     
    #include "icrsint.h" 
     
    //This class extracts LastName,Country,FirstName from Employees table 
     
    class CEmployeeRs : public CADORecordBinding 
    { 
    BEGIN_ADO_BINDING(CEmployeeRs) 
     // Column LastName is the 2nd field in the table 
     ADO_VARIABLE_LENGTH_ENTRY2(2,adVarChar,m_szemp_LastName, 
     sizeof(m_szemp_LastName),lemp_LastNameStatus,TRUE) 
     // Column Country is the 11th field in the table 
     ADO_VARIABLE_LENGTH_ENTRY2(11,adVarChar,m_szemp_Country, 
     sizeof(m_szemp_Country),lemp_CountryStatus,TRUE) 
     // Column Country is the 17th field in the table 
     ADO_VARIABLE_LENGTH_ENTRY2(17,adVarChar,m_szemp_FirstName, 
     sizeof(m_szemp_FirstName),lemp_FirstNameStatus,TRUE) 
    END_ADO_BINDING() 
     
    public: 
     CHAR m_szemp_LastName[21]; 
     ULONG lemp_LastNameStatus; 
     CHAR m_szemp_Country[16]; 
     ULONG lemp_CountryStatus; 
     CHAR m_szemp_FirstName[11]; 
     ULONG lemp_FirstNameStatus; 
    }; 
    // EndIndexNullsH